1. Field of the Invention
The present invention relates to a coplanar waveguide that can be applied to a high-speed optical communication module using a high radio frequency, and more particularly, to a coplanar waveguide that can change the propagation direction of a high-speed frequency signal at several tens GHz or more with a minimum loss and an optical communication module using the coplanar waveguide.
2. Discussion of Related Art
In recent years, as communication traffic increases, a high-speed radio frequency (RF) signal needs to be efficiently transmitted with a minimum loss. In some cases, a propagation direction of RF needs to be changed to 90° or another angle. In particular, in fabricating a module for optical communication, the RF propagation direction needs to be changed so that the RF direction becomes parallel to a light direction.
A coplanar waveguide is a transmission line that is generally used to efficiently transmit a high frequency at a very high speed. A method with a chamfered corner of a metal pattern of a coplanar waveguide in order to change the propagation direction of RF traveling along the coplanar waveguide on the same plane is disclosed in U.S. Patent Laid-Open Publication No. 2003/0202800A1.
In the U.S. patent publication, metal patterns 1, 2 and 3 have a chamfered corner in order to change the RF propagation direction by 90°, as indicated by reference mark A in FIG. 7. Therefore, it is possible to compensate for excessive electrical capacitance created as the RF propagation direction is changed, and to efficiently transmit a high frequency signal at a frequency band of several GHz.
However, one simulation showed that the coplanar waveguide according to the U.S. patent publication cannot be used as a transmission line for 40 GHz or more optical communication because it has a too great reflection loss in the 40 GHz or more optical communication. The conventional art is limited to a frequency band of about 20 GHz, and thus cannot be applied to an optical communication module at a frequency band of 40 GHz that the present invention pertains to.
As another conventional art, there is a method for additionally attaching three-dimensional air bridges B and C to bent portions of a coplanar waveguide, as illustrated in FIG. 8. The conventional art additionally requires micro electro mechanical systems (MEMS) or processes such as electroplating, vacuum deposition, and the like in order to attach the air bridges in fabricating the coplanar waveguide. This makes it difficult to fabricate the coplanar waveguide and significantly increases a coplanar waveguide fabrication cost.